Switched mode power supplies (SMPS), such as buck converters, boost converters, buck-boost converters and flyback converters perform alternating current (AC) to direct current (DC) conversions as well as DC to DC conversions with voltage level transformations from input to output. These types of power supply converters generally employ switching devices such as bipolar junction transistors (BJTs) or metal oxide semiconductor field effect transistors (MOSFETs) where the switching frequencies and pulse widths are modulated to control operational parameters of the converter.
The use of BJTs instead of MOSFETs in the converter design can result in reduced cost and increased efficiency in higher voltage applications, for example greater than 700 volts. BJTs, however, generally have slower switching speeds than MOSFETs and therefore cannot operate in the higher frequency ranges that are required for some applications. BJTs also require greater control over the gate drive biasing to reduce switching losses, saturation losses and storage time, which can be difficult to achieve.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art.